An analog-to-digital (A/D) converter is a circuit on the borderline between the analog domain and the digital domain which acts as an intermediary in the exchange of information between the two domains. As the name indicates, an A/D-converter converts or transforms analog input signals to digital output signals. An A/D-converter could be used for converting analog information such as audio signals or measurements of physical variables into numbers consisting of two-level digits or bits; a form suitable for digital processing. A/D-converters are found in numerous applications of all modern technologies. They are widely used in different fields of electronics and communication.
The accuracy of an A/D-converter naturally determines to what extent the digital output signal truly represents the analog input signal. The performance evaluation of an A/D-converter with regard to accuracy and distortion is normally based on the magnitude of the error generated in the A/D-conversion. In general, all A/D-converters suffer from offset errors due to imperfections in the circuit realizations of the converters. These offset errors will influence the behavior and performance of the A/D-converter.
A particular type of A/D-converter is the cyclic A/D-converter which utilizes the same functional blocks cyclically for bit-wise generation of all the bits of a digital output value. Conventionally, cyclic A/D-converters are constructed to generate digital output signals of regular binary code. In these conventional binary code cyclic A/D-converters, the offset errors propagate and accumulate in a strictly increasing manner during a conversion, thus limiting the accuracy of the converter and increasing the distortion. Relatively large differential and integral non-linearities will be introduced, and in the worst case scenario some output codes might be missing.